Dense Phase Swirl Pulverized Coal Burner

ABSTRACT

A dense phase swirl pulverized coal burner comprises a primary air channel, a direct flow secondary air channel and a outermost swirl secondary air channel; and multiple levels of pulverized coal concentration rings are arranged axially at intervals along the oil gun casing in a straight tube section of the primary air channel, so that pulverized coal air flow is distributed thickly outside and thinly inside the primary air nozzle. In the invention, dense phase pulverized coal outside the primary air nozzle passes through guide vanes, forms disturbed flow, is ejected into a furnace and mixes with high temperature backflow flue gas rapidly and sufficiently at an outlet. Meanwhile, dilute pulverized coal air flow at the center is ejected into the furnace by direct flow, ensuring subsequent mixing and combustion of pulverized coal flow. The primary air nozzle and the secondary air nozzle are provided with cone flaring structures with certain angle to effectively control appropriate mixing of secondary air and pulverized coal. The invention has advantages of strong ignition and combustion stability, good coal adaptability, low nitric oxide emission, simple primary air channel structure and small resistance, which effectively slows wear rate of parts.

FIELD OF THE INVENTION

The invention relates to the technical field of coal fired boilers inpower plants, in particular to a dense phase swirl pulverized coalburner used for a coal-fired boiler.

DESCRIPTION OF THE RELATED ART

As nitric oxide emissions from boilers of coal-fired power plants arestrictly controlled in China in recent years, a supporting low NOxburner technology of full furnace staged combustion low NOX technologyis widely used, particularly various different low NOx swirl burnertechnologies in wall-fired boilers.

In order to effectively reduce nitric oxides produced from combustion ina furnace of a wall-fired boiler, for the full furnace staged combustiontechnology, part of oxygen that is delivered from a main combustion zoneto realize burning-out in early technologies (i.e. pulverized coal issent to a burner zone of the furnace, hereinafter referred to as themain combustion zone) is supplied to the furnace through a special airport at the upper part of the furnace in a delayed manner, thus formingoxygen-deficient combustion atmosphere when chemical equivalent ratio ofair in the main combustion zone is less than 1 and forming a reducingatmosphere area between the main combustion zone and the upper air port(burning-out zone), which allows sufficient reduction of early nitricoxides. Meanwhile, most of the swirl burners are subject to rich-leancombustion and multichannel grading air supply mode so as to controlmixing time of air and pulverized coal, form the reducing atmosphere inthe burner zone and achieve the purpose of reducing nitric oxides in theburner zone.

However, 3 issues exist for application of the burner technology: 1, inorder to divide pulverized coal air flow in the primary air channel intodense flow and thin flow circumferentially, uniformly and effectively,the burner always has relatively complex structure, which may increasesystem resistance, increase fan load and house supply, wear the channel,shorten life cycle of equipment and increase operation and maintenancecost of power plants; 2, due to poor adaptability of coal, particularlypoor steam coal in China, actual coal ignition and combustion stabilitycan not reach original design requirements, and flame at outlet of theburner is always unstable during peak regulation of the boiler; and 3,due to poor subsequent mixing performance of primary air pulverized coalair flow and secondary air pulverized coal air flow at the nozzle of theburner, coal in the burner cannot be burnt out, possibly increasingloss.

SUMMARY OF THE INVENTION

The purpose of the invention is to provide a dense phase swirlpulverized coal burner used for a coal-fired boiler of a power plant.The dense phase swirl pulverized coal burner can enhance mixing of densephase pulverized coal air flow and outlet high temperature backflow withthe help of dense phase pulverized coal disturbed flow at a nozzle torealize rapid ignition and stable combustion of pulverized coal, andcontrol appropriate mixing of secondary air and primary air so as toenhance subsequent mixing and burning-out of the pulverized coal airflow. Besides, a pulverized coal concentration ring inside a primary airchannel has simple structure and small resistance, effectively slowingwear rate and extending use and maintenance period of equipment.

In order to achieve the purpose, the technical solution of the inventionis to provide a dense phase swirl pulverized coal burner whichcomprises:

a primary air channel provided with the following parts communicatedsuccessively: an elbow section as a pulverized coal inlet, a straighttube section arranged horizontally and a primary air nozzle; and an oilgun casing arranged on a central shaft of the straight tube section andan torch oil gun of a burner arranged inside the oil gun casing;

a direct flow secondary air channel arranged around outer wall of anozzle of the primary air channel, and a swirl secondary air channelarranged around outer wall of a nozzle of the direct flow secondary airchannel with the direct flow secondary air channel and the swirlsecondary air channel distributed with air in a same big wind box; aregulating device arranged in the direct flow secondary air channel forregulating air flow; and a regulating device arranged in the swirlsecondary air channel for regulating swirl air strength.

The elbow section of the primary air channel is provided with apulverized coal flow equalizing plate arranged around the central shaftof the elbow section and divided into two-layer air channels in theelbow section; one end of the pulverized coal flow equalizing plate isarranged at an inlet of the elbow section and the other end thereofextends to an outlet of the elbow section, i.e. the positioncommunicating the elbow section with the straight tube section, so thatthe pulverized coal air flow passes through the elbow section to bedistributed uniformly and circumferentially, and enters the straighttube section.

Multiple levels of pulverized coal concentration rings are arrangedaxially at intervals along the oil gun casing in the straight tubesection of the primary air channel; and each level of pulverized coalconcentration ring is a cone flaring structure arranged around outeredge of the oil gun casing, and a cone flaring opening thereof faces theprimary air nozzle so as to allow the pulverized coal air flow to bedistributed thickly outside and thinly inside the primary air nozzleafter being subject to multiple levels of cone flaring.

Preferably, the oil gun casing of the straight tube section is providedwith 2-3 levels of pulverized coal concentration rings, and size of thepulverized coal concentration rings is enlarged by levels. Cone flaringangle of each level of pulverized coal concentration rings is within therange of 10°-25°.

The nozzle of the primary air channel is provided with multiple guidevanes arranged uniformly and circumferentially around inner wallthereof; the guide vanes have positions matched with path field of densephase pulverized coal air flow outside the nozzle, and disturbperipheral dense phase pulverized coal only, thus allowing the densephase pulverized coal air flow to eject at a certain swirl angle; anddilute phase pulverized coal air flow at center of the nozzle will beejected into an external furnace directly.

Preferably, the nozzle of the primary air channel is provided with 10-20guide vanes (7) around inner wall thereof An included angle between eachof the guide vanes and axial direction of the primary air channel is10°-30°, and radial height of the guide vanes along the primary airchannel is 0.05-0.1 time diameter of the primary air channel.

Outer walls of the nozzles of the primary air channel, the direct flowsecondary air channel and the swirl secondary air channel arerespectively provided with the flow expanding cone structures, and coneflaring openings thereof are respectively arranged toward the externalfurnace to delay mixing time of secondary air and primary air.

Preferably, the cone flaring angles of the multiple flow expanding conestructures are not more than 45°.

Compared with the prior art, the dense phase swirl pulverized coalburner of the invention has advantages that the primary air passesthrough the pulverized coal flow equalizing plate and forms relativelyuniform two layers around the air channel; due to effect of the multiplelevels of pulverized coal concentration rings in the horizontal straighttube section, the primary air can distribute thickly outside and thinlyinside the primary air nozzle under the action of cone flaring.

As the flow expanding cone structures are arranged on the primary airnozzle and the secondary air nozzle respectively, mixing time of thesecondary air and the primary air is delayed under the action of coneflaring. Based on reasonable control of the cone flaring angles, anoxygen-deficient atmosphere is formed in the primary air during initialignition, which allows sufficient reduction of early nitric oxides.Appropriate mixing of the primary air and the secondary air can keepwater cooled walls of the nozzles to be in an oxidizing atmosphere for along time, effectively preventing clogging and high temperaturecorrosion of the water cooled wall of the burner zone.

Besides, due to cone flaring effect of the primary air nozzle, a hightemperature flue gas backflow area is formed around the nozzle; andmultiple guide vanes are arranged on the inner wall of the nozzle of theprimary air channel to disturb the dense phase pulverized coal beforebeing ejected into the furnace and eject the dense phase pulverized coalinto the high temperature flue gas backflow area at a certain swirlangle for strong mixed combustion, thereby achieving the purpose ofrapid ignition and enhancing stable combustion.

In addition, dilute phase pulverized coal at the center of the primaryair nozzle is ejected into the furnace by direct flow, which keepsrigidity of the primary air and allows thorough mixing and burning-outof the subsequent primary air and secondary air.

Therefore, the invention can be strongly adaptable to various types ofcoal. For different coal types, the cone flaring angles and gradingarrangement of the pulverized coal concentration rings can be designedto control dense and dilute separation degree of pulverized coal; radialheight of the guide vanes and size of the included angles between theguide vanes and the axial direction can be designed to control disturbedflow of dense phase pulverized coal; and the flow expanding conestructure of the primary air nozzle can be used to control size of thehigh temperature backflow area. According to change of coal qualityduring operation, swirl intensity of the secondary air can be regulatedby the regulating device to adapt to ignition and stable combustionrequirements of different types of coal.

The invention is characterized by simple primary air channel structure,good wear resistance, strong overall ignition and stable combustion,good coal adaptability, high efficiency and low nitric oxide emission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an overall structure of the dense phaseswirl pulverized coal burner in the invention; and

FIG. 2 is a schematic diagram of structural layout of guide vanes of anozzle of the dense phase swirl pulverized coal burner in the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will be described in combination with accompanieddrawings.

As shown in FIG. 1, the dense phase swirl pulverized coal burner of theinvention (hereinafter referred to as the burner) comprises a primaryair channel 1, a direct flow secondary air channel 2 arranged aroundouter wall of a nozzle of the primary air channel 1, and a swirlsecondary air channel 3 arranged around outer wall of a nozzle of thedirect flow secondary air channel 2. The direct flow secondary airchannel 2 and the swirl secondary air channel 3 are distributed with airin a same big wind box.

The primary air channel 1 is provided with the following partscommunicated successively: an elbow section as a pulverized coal inlet,a straight tube section arranged horizontally and a primary air nozzle.An oil gun casing 4 is arranged on a central shaft of the straight tubesection of the primary air channel 1, and a torch oil gun of the burneris arranged inside the oil gun casing 4.

The elbow section of the primary air channel 1 is provided with apulverized coal flow equalizing plate 5 arranged around the centralshaft of the elbow section and divided into interior and exteriortwo-layer air channels near and far from a turning center in the elbowsection; one end of the pulverized coal flow equalizing plate 5 isarranged on an inlet of the elbow section, and the other end thereofextends to an outlet of the elbow section, i.e. the positioncommunicating the elbow section with the straight tube section.Therefore, when primary air pulverized coal air flow passes through theelbow section of the primary air channel 1, the pulverized coal flowequalizing plate 5 and the horizontal straight tube section to formupper and lower two-layer uniform air flow, thus ensuring thatpulverized coal is relatively circumferential and uniform at the outletof the elbow section.

Further, 2-3 levels of pulverized coal concentration rings 6 arearranged axially at intervals along the oil gun casing 4 in thehorizontal straight tube section of the primary air channel 1; and eachlevel of pulverized coal concentration rings 6 is a cone flaringstructure arranged around outer edge of the oil gun casing 4, a coneflaring opening thereof faces the nozzle, and cone flaring angles α ofthe pulverized coal concentration rings is within the range of 10°-25°;and size of the pulverized coal concentration rings 6 is enlarged bylevels. After the pulverized coal air flow uniformly distributed in thestraight tube section under the action of the pulverized coal flowequalizing plate 5 successively passes through the cone flaringstructures of each of pulverized coal concentration rings 6, mostpulverized coal air flow will be kept in the straight tube section ofthe primary air channel 1 due to inertia, flow from the periphery of thecentral shaft, and finally be distributed thickly outside and thinlyinside the nozzle of the primary air channel 1.

As shown in FIG. 1 and FIG. 2, the nozzle of the primary air channel 1is provided with multiple guide vanes 7 arranged uniformly andcircumferentially around inner wall thereof (10-20 vanes); an includedangle between each of the guide vanes 7 and axial direction of theprimary air channel 1 is 10°-30°, and radial height of the guide vanesalong the primary air channel 1 is 0.05-0.1 time diameter of the primaryair channel 1. That is, THE multiple guide vanes 7 are arranged on anarea at the periphery of the channel where the dense phase pulverizedcoal flows; dense phase flow is disturbed to eject at a certain swirlangle before being ejected into the furnace, and the dilute phasepulverized coal air flow at the center is still ejected into the furnacealong the axis of the channel by direct flow.

Flow expanding cone structures facing one end of the furnace andcorresponding to serial number 8, 9 and 10 in FIG. 1 are arranged onouter walls of the nozzles of the primary air channel 1, the direct flowsecondary air channel 2 and the swirl secondary air channel 3respectively, thus delaying mixing time of the secondary air and theprimary air under the action of cone flaring. Based on reasonablecontrol of the cone flaring angles, an oxygen-deficient atmosphere canbe formed in the primary air during initial ignition, which allowssufficient reduction of early nitric oxides. The preferred cone flaringangles β1, β2 and β3 corresponding to the flow expanding cone structures8, 9 and 10 are not more than 45° respectively.

In addition, negative pressure is produced due to arrangement of theflow expanding cone structure 8 in the burner, and the nozzle of theprimary air channel 1 entrains high temperature flue gas to form anannular high temperature flue gas backflow area. Thus, the dense phasepulverized coal air flow at the periphery of the primary air nozzle isdisturbed by the guide vanes 7 and ejected into the high temperatureflue gas backflow area to strongly mix with air there, which can causerise temperature of the pulverized coal sharply due to great heat andignite the pulverized coal for a moment.

In addition, according to arrangement of the flow expanding conestructures 8 and 9, the direct flow secondary air channel 2 and theswirl secondary air channel 3 are provided with regulating devices 11and 12 respectively for controlling air flow and swirl air strength tocontrol mixing time of the secondary air and the primary air.Appropriate mixing of the primary air and the secondary air can allowwater cooled walls of the nozzles to be in an oxidizing atmosphere for along time, effectively preventing clogging and high temperaturecorrosion of the water cooled wall of the burner zone.

Besides, the dilute phase pulverized coal air flow at the center of theprimary air nozzle is directly ejected into the furnace along the axisof the channel without disturbed flow, which can keep rigidity of theprimary air and ensure that the primary air is ejected into a certainlydeep position in the furnace. Subsequently, due to disturbed flow of theswirl secondary air, the pulverized coal air flow is strongly mixed toensure subsequent mixing and combustion of the pulverized coal air flow,reduce nitric oxides in the burner during initial oxygen-deficientcombustion and achieve the purpose of efficient burning-out of thepulverized coal.

Therefore, the invention can be strongly adaptable to various types ofcoal. For different types of coal, the cone flaring angle and gradingarrangement of the pulverized coal concentration rings 6 can be designedto control dense and dilute separation degree of the pulverized coal;radial height of the guide vanes 7, and size of the included anglebetween the guide vanes 7 and the axial direction can be designed tocontrol disturbed flow of the dense phase pulverized coal; and the flowexpanding cone structure 8 of the primary air nozzle can be used tocontrol the size of the high temperature backflow area. According tochanges of coal quality during operation, swirl intensity of thesecondary air can be regulated by the regulating devices 11, 12 to adaptto ignition and stable combustion requirements of different types ofcoal.

The invention is characterized by simple structure, good wearresistance, strong ignition and stable combustion, good coaladaptability, high efficiency and low nitric oxide emission.

While the invention has been described in detail and with reference tothe preferred embodiment, it is to be understood that the invention isnot restricted thereto. It is apparent to those skilled in the art thatvarious changes and modifications can be made therein in accordance withthe disclosure. Therefore, scope of the invention is to be restrictedonly by the appended claims.

1. A dense phase swirl pulverized coal burner, characterized by comprising a primary air channel (1) provided with the following parts communicated successively: an elbow section as a pulverized coal inlet, a straight tube section arranged horizontally and a primary air nozzle; and an oil gun casing (4) arranged on a central shaft of the straight tube section and a torch oil gun of the burner arranged inside the oil gun casing (4); a direct flow secondary air channel (2) arranged around outer wall of the nozzle of the primary air channel (1), and a swirl secondary air channel (3) arranged around outer wall of a nozzle of the direct flow secondary air channel (2) with the direct flow secondary air channel (2) and the swirl secondary air channel (3) distributed with air in a same big wind box; wherein, multiple levels of pulverized coal concentration rings (6) are arranged axially at intervals along the oil gun casing (4) in the straight tube section of the primary air channel (1); and each level of the pulverized coal concentration rings (6) is a cone flaring structure arranged around outer edge of the oil gun casing (4), and a cone flaring opening thereof faces the primary air nozzle so that pulverized coal air flow is distributed thickly outside and thinly inside the primary air nozzle after being subject to multiple levels of cone flaring.
 2. The dense phase swirl pulverized coal burner according to claim 1, characterized in that the elbow section of the primary air channel (1) is provided with a pulverized coal flow equalizing plate (5) arranged around the central shaft of the elbow section and divided into two-layer air channels in the elbow section; one end of the pulverized coal flow equalizing plate (5) is arranged on an inlet of the elbow section, and the other end thereof extends to an outlet of the elbow section, i.e. the position communicating the elbow section with the straight tube section so that the pulverized coal air flow passes through the elbow section, is distributed uniformly and circumferentially, and enters the straight tube section.
 3. The dense phase swirl pulverized coal burner according to claim 1, characterized in that the nozzle of the primary air channel (1) is provided with multiple guide vanes (7) arranged uniformly and circumferentially around inner wall thereof; positions of the guide vanes (7) are matched with path field of the dense phase pulverized coal air flow so that the dense phase pulverized coal air flow forms disturbed flow and is ejected at a certain swirl angle; and dilute phase pulverized coal air flow at the center of the nozzle is ejected into an external furnace directly.
 4. The dense phase swirl pulverized coal burner according to claim 1, characterized in that outer walls of the nozzles of the primary air channel (1), the direct flow secondary air channel (2) and the swirl secondary air channel (3) are provided with flow expanding cone structures (8, 9, 10) respectively; and cone flaring openings of the flow expanding cone structures (8, 9, 10) are respectively arranged toward the external furnace so as to delay mixing time of secondary air and primary air.
 5. The dense phase swirl pulverized coal burner according to claim 1, characterized in that the oil gun casing (4) of the straight tube section is provided with 2-3 levels of pulverized coal concentration rings (6), and size of the pulverized coal concentration rings (6) is enlarged by levels.
 6. The dense phase swirl pulverized coal burner according to claim 5, characterized in that a cone flaring angle (α) of each level of the pulverized coal concentration rings (6) is within the range of 10°-25°.
 7. The dense phase swirl pulverized coal burner according to claim 3, characterized in that the nozzle of the primary air channel (1) is provided with 10-20 guide vanes (7) around inner wall thereof.
 8. The dense phase swirl pulverized coal burner according to claim 7, characterized in that an included angle between each of the guide vanes (7) and axial direction of the primary air channel (1) is 10°-30°, and radial height of the guide vanes (7) along the primary air channel (1) is 0.05-0.1 time the diameter of the primary air channel (1).
 9. The dense phase swirl pulverized coal burner according to claim 4, characterized in that cone flaring angles (β1, β2, β3) of the multiple flow expanding cone structures are not more than 45° respectively.
 10. The dense phase swirl pulverized coal burner according to claim 1, characterized in that the direct flow secondary air channel (2) is provided with a regulating device (11) for regulating air flow; and the swirl secondary air channel (3) is provided with a regulating device (12) for regulating swirl air strength. 